In kitchens for restaurants or other institutional feeding places, creature comfort plus local safety codes frequently call for venting system for positive removal of the cooking fumes for discharge to atmosphere outside the kitchen. Because of the generation in these fumes of vaporous grease, it is further generally required to filter or extract the grease from the vented air before discharging it to atmosphere. Two basic types of grease extraction systems are employed, the filtering system and the centrifical flow system.
The filtering system requires that the vented air pass through very finely meshed media that allows through passage of only particles smaller than the mesh openings of the media. Droplets of grease, typically having a larger micron diameter than the media flow paths, are thus removed from the airstream and collected on the media. The problem with these filters is that increased back pressure is generated as the filters become dirty, thereby decreasing the volume of the vented air below that actually needed or desired. Further, the filters have to be cleaned or replaced on a very regular basis, or they become grease entrained so as to create a fire hazard.
The centrifugal flow system relies soley on creating a tortuous path for the vented air to follow, so that each time the air is forced to bend the heavier droplets of grease are thrown against the wall defining the tortuous path and thereby removed from the airstream. The grease droplets generally accumulate in sufficient volumes that most of that collected can be drained along pitched walls and be discharged to a collector. However, a problem again exists in the system in that the surfaces must be periodically cleaned to prevent a fire hazard as well as keep the back pressure against flow within specific limits. In some designs, small separate louver elements are used to create the tortuous flow paths and these must be removed from the vent structure and be washed by hand . . . a potentially haphazard or unreliable, time consuming, and costly procedure. In certain other designs, the vent structure itself defines the extractor, and internally located nozzles can discharge hot water and detergent to remove the bulk of the grease off the surfaces of the vent walls; but known systems provide incomplete wash coverage. Further, unitary vent extractor arrangements of this type typically must have a damper that can be shifted to block off the flow path in case of a fire, and incomplete wash coverage can allow such grease buildup to preclude or hinder the closing operation of the damper.
Several patents which relate to the ventilation apparatus over which the disclosure forms an improvement are the Gaylord U.S. Pat. No. 2,813,477 entitled Safety Ventilator Unit; the Graswich et al. U.S. Pat. No. 2,961,941 entitled Grease Extracting Attachment for Ventilators for Kitchen Ranges; the Gaylord U.S. Pat. No. 3,055,285 entitled Kitchen Ventilating System; the Gaylord U.S. Pat. No. 3,207,058 entitled Kitchen Ventilating System; the Gaylord U.S. Pat. No. 3,247,776 entitled Kitchen Ventilating System; the Gaylord U.S. Pat. No. 3,611,909 entitled Fail-Safe Damper Control for Kitchen Ventilator; and the Gaylord U.S. Pat. No. 3,785,124 entitled Pollution-Free Kitchen Ventilator.